Yongming Shen

Three-dimensional simulation of meandering river based on 3-D RNG κ-ɛ turbulence model

A 3-D numerical model for calculating flow in non-curvilinear coordinates was established in this article. The flow was simulated by solving the full Reynolds-averaged Navier-Stokes equations with the RNG k-ε turbulence model. In the horizontal x-y-plane, a boundary-fitted curvilinear co-ordinate system was adopted, while in the vertical direction, a σco-ordinate transformation was used to represent the free surface and bed topography. The water level was determined by solving the 2-D Poisson equation derived from 2-D depth averaged momentum equations. The finite-volume method was used to discretize the equations and the SIMPLEC algorithm was applied to acquire the coupling of velocity and pressure. This model was applied to simulate the meandering channels and natural rivers, and the water levels and the velocities for all sections were given. By contrasting and analyzing, the agreement with measurements is generally good. The feasibility studies of simulating flow of the natural river have been conducted to demonstrate its applicability to hydraulic engineering research.

Flow structure and sediment transport with impacts of aquatic vegetation

Aquatic vegetation plays an important role in the flow structure of open channels and thus changes the fate and the transport of sediment. This article proposes a three-dimensional turbulence model by introducing vegetation density and drag force into the control equations of water flow in the presence of vegetation. The model was used to calculate the impacts of submerged vegetation on the vertical profiles of longitudinal flow velocities, the changes of the depth-averaged flow velocities in a compound channel with emergent vegetation in the floodplain, the removal of suspended sediment from the channels by emergent vegetation, and the bed changes around and in a vegetated island. Numerical investigations show that aquatic vegetation retards flow in the vegetation zone, reduces the sediment transport capacity, and contributes to erosion on both sides of the vegetated island. Calculated results agree well with experimental results.

DEVELOPMENT AND APPLICATION OF A EUTROPHICATION WATER QUALITY MODEL FOR RIVER NETWORKS

The Preissmann implicit scheme was used to discretize the one-dimensional Saint-Venant equations, the river-junction-river method was applied to resolve the hydrodynamic and water quality model for river networks, and the key issues on the model were expatiated particularly in this article. This water quality module was designed to compute time dependent concentrations of a series of constituents, which are primarily governed by the processes of advection, dispersion and chemical reactions. Based on the theory of Water Quality Analysis Simulation Program (WASP) water quality model, emphasis was given to the simulation of the biogeochemical transformations that determine the fate of nutrients, in particular, the simulation of the aquatic cycles of nitrogen and phosphorus compounds. This model also includes procedures for the determination of growth and death of phytoplankton. This hydrodynamic and water quality model was applied to calculate two river networks. As illustrated by the numerical examples, the calculated water level and discharge agree with the measured data and the simulated trends and magnitudes of water quality constituents are generally in good agreement with field observations. It is concluded that the presented model is useful in the pollutant control and in the determination of pollutant-related problems for river networks.

Study and Application of Steady Flow and Unsteady Flow Mathematical Model for Channel Networks

Based on the Preissmann implicit scheme for the one-dimensional Saint-Venant equation, the mathematical model for one-dimensional river networks and canal networks was developed and the key issues on the model were expatiated particularly in this article. This model applies the method of three-steps solution for channel-junction-channel to simulate the river networks, and the Gauss elimination method was used to calculate the sparse matrix. This model was applied to simulate the tree-type irrigation canal networks, complex looped channel networks and the Lower Columbia Slough networks. The results of water level and discharge agree with the data from the Adlul and field data. The model is proved to be robust for simulating unsteady flows in river networks with various degrees of complex structure. The calculated results show that this model is useful for engineering applications in complicated river networks. Future research was recommended to focus on setting up ecological numerical model of water quality in river networks and canal networks.

Numerical study of wave and longshore current interaction

Wave and longshore current interaction was examined based on the numerical models. In these models, water waves in the presence of longshore currents were modeled by parabolic mild slope equation, and wave breaking induced longshore currents were modeled by shallow water equation. Water wave provided the radiation stress gradients to drive current. Wave and longshore current interactions were considered by cycling the wave and longshore current models to a steady state. The experiments for regular and irregular breaking wave induced longshore currents by Hamilton and Ebersole (2001) and Reniers and Battjes (1997) were simulated. The numerical results indicate that the present models are effective for simulating the interaction of wave and breaking wave induced longshore currents, and the numerically simulated longshore current at wave breaking point considering wave and longshore current interaction show some disagreement with those neglecting the wave-current interaction, and the breaking wave induced longshore current effect on wave transformation is not obvious.

3D numerical modeling of non-isotropic turbulent buoyant helicoidal flow and heat transfer in a curved open channel

Abstract A 3D non-isotropic algebraic stress/flux turbulence model is employed to simulate turbulent buoyant helicoidal flow and heat transfer in a rectangular curved open channel. The prediction shows that, unlike the isothermal flow, there are two major and one minor secondary flow eddies in a cross section of thermally stratified turbulent buoyant helicoidal flow in a curved open channel. The results compare favorably with available experimental data. The thermocline in a curved channel is thicker than that in a straight channel. All of these is the result of complex interaction between the buoyant force, the centrifugal force and the Reynolds stresses. The turbulent flow in a curved channel is obviously non-isotropic: the turbulence fluctuations in vertical and radial directions are lower in magnitude than that in the axial direction, which illustrates the suppression of turbulence due to buoyant and centrifugal forces. The results are of significant practical value to engineering works such as the choice of sites for intake and pollutant-discharge structures in a curved river.

A three-dimensional numerical model of hydrodynamics and water quality in Hakata Bay

The hydrodynamics and water quality in Hakata Bay, Japan, are strongly affected by the seasonal variations in both the gravitational circulation and the stratification in the bay. The three-dimensional hydrodynamics and water quality model has been developed to simulate the long-term transport and fate of pollutants in the system. The model is unique in that it completely integrates the refined modelling of the hydrodynamics, biochemical reactions and the ecosystem in the coastal areas. It is a 3-dimensional segmented model which is capable of resolving mean daily variations in all the parameters relevant to pollution control. It predicts daily fluctuations in the oxygen content at different depths in water throughout the year. It takes into account transport and settling of pollutant particles. It predicts light penetration from computed turbidity variations. It includes interactions between the ecosystem and water quality, through nutrient cycling and photosynthesis. The model has been calibrated well against the data set of historical water quality observations in Hakata Bay.

Numerical simulation of long-shore currents induced by regular breaking wave

Abstract The hydrodynamics of coastal zones are extremely complicated, being influenced greatly by shallow water waves and currents induced by wave breaking. This paper presents numerical simulations of long-shore currents induced by the breaking of oblique incident waves in shallow coastal zones. The wave numerical model is based on parabolic mild slope equation, and so the wave radiation stress required for the generation of wave-induced currents are calculated based on the variables in the parabolic mild slope equation, and the long-shore currents have been numerically simulated based on these. The numerical models are validated against experimental data, and the results suggest that the long-shore current velocity and wave set-up increase with the increasing incident wave amplitude and offshore slope steepness, as well as the wave set-up increase with the increasing incident wave period.

WATER WAVE SIMULATION IN CURVILINEAR COORDINATES USING A TIME-DEPENDENT MILD SLOPE EQUATION *

The purpose of this article is to model the detailed progress of wave propagation in curvilinear coordinates with an effective time-dependent mild slope equation. This was achieved in the following approach, firstly deriving the numerical model of the equation, i.e., Copeland’s hyperbolic mild-slope equation, in orthogonal curvilinear coordinates based on principal of coordinate transformation, and then finding the numerical solution of the transformed model by use of the Alternative Directions Implicit (ADI) method with a space-staggered grid. To test the curvilinear model, two cases of a channel with varying cross section and a semi-circular channel were studied with corresponding analytical solutions. The model was further investigated through a numerical simulation in Ponce de Leon Inlet, USA. Good agreement is reached and therefore, the use of the present model is valid to calculate the progress of wave propagation in areas with curved shorelines, nearshore breakwaters and other complicated geometries.

Modeling Near-Shore Currents Induced by Irregular Breaking Wave

Abstract Near-shore surface water waves and wave-induced currents are important hydrodynamic factors in coastal zones. Propagation of irregular water waves and irregular breaking-wave induced near-shore currents have been numerical studied based on parabolic mild slope equation and near-shore currents model. Based on the JOSNWAP wave spectrum, the parabolic mild slope equation incorporating irregular and wave-breaking effects have been applied to model water waves. The wave radiation stresses exerted on currents have been calculated based on variables in the parabolic mild slope equation, and near-shore wave-induced currents have been numerically simulated based on these. The numerical results have also been validated and analyzed. It is believed that the presented numerical models are capable of adaptation to numerical simulating wave-induced near-shore circulation.